Engines may utilize recirculation of exhaust gas from an engine exhaust system to an engine intake system, a process referred to as exhaust gas recirculation (EGR), to reduce regulated emissions. In some examples, one or more valves may control the flow of exhaust gas in the EGR system. Additionally, engines may utilize one or more turbochargers to increase the power provided by the engine. Turbochargers function by compressing intake air in a compressor via a turbine operated by exhaust gas flow. Turbocharged engines may utilize one or more bypass valves to control the flow through the turbocharger. As such, EGR flow and exhaust flow are controlled by several valves. The position and function of theses valves may be monitored in order to reduce emission violation and maintain engine performance.
In one example, the function of the EGR and turbocharger bypass valves may be diagnosed by valve position feedback sensors. However, such sensors are expensive and may increase the complexity of engine control routines. Additionally, these sensors may not accurately indicate all types of valve degradation; thus, valve diagnosis may be limited.